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[en] The analysis of dose-effect relationships was carried out by taking into account individual frequencies of cytogenetic damages (chromosome aberrations and polyploid cells in bone marrow as well as micro nucleated erythrocytes in bone marrow and peripheral blood) and individual radiation exposure. The objects of investigations were bank voles (Clethrionomys glareolus) inhabited radio contaminated regions of Belarus and laboratory mice exposed in these regions in the conditions of external and internal irradiation. The frequencies of cytogenetic damages were the first revealed to depend on low levels of exposure: concentration of basic dose-forming radionuclides (4-145410 Bq/kg of ¹³⁷Cs and ¹³⁴Cs), total absorbed dose rate (2-730 mGy/day) and the total absorbed dose (0.02-7.3 cGy). According to the latest information on cancerous and non-cancerous risks acquired by survivors of nuclear bombardments, significant effects of acute irradiation were observed in the range of 0.005-0.2 Sv. Our findings demonstrate effects of chronic irradiation in much lower range and indicate the absence of threshold of low dose impact. For comparing effectiveness of chronic and acute irradiation, the dose-effect curves of acute irradiation (10-100 cGy) were obtained for bank voles from two chronically irradiated populations. Extrapolation of the obtained dose-effect straight lines to the dose range of chronic irradiation has shown their much higher efficiency as against low doses of acute irradiation. Possible causes of such disagreement are discussed. (authors)

[en] The study provides the date which was obtained on many generations (1 - 22) of small mammals from natural populations exposed to chronic low-dose irradiation after the Chernobyl accident. The frequency of micronucleus in the polychromatophile (immature) erythrocytes of the marrow was determined. This method is simple but rather informative for the determination of the level of the mutation process. The state of the erythropoiesis was estimated as a relation of the count of the polychromatophile to normal chromatophile (mature) erythrocytes in the marrow. While the radiation load on animals was reduced during the whole period under investigation (1986 - 1996) the increased levels of the mutation process in the somatic cells as well as the changes in erythropoiesis were revealed

[en] Full text: The long-term course of the radionuclide activity concentration by natural populations of small mammals (bank vole and yellow necked mice) over 1986-1998 were established; the whole-body absorbed doses of external and internal irradiation with incorporated radionuclides were calculated; and time-course of whole-body absorbed dose rates and absorbed doses over 20-22 bank vole generations was determined. Genetic effects of low-dose chronic irradiation were proved in the range from close to background doses up to 10 cGy for germ and somatic cells of bank vole whose populations inhabited contaminated areas within 20-22 generations, as well as for germ and somatic cells of laboratory mice and pond carp. The recent general report on cancer incidence data in the cohort of atomic bomb survivors followed up by the Radiation Research Foundation give strong evidence that there is direct, statistically significant evidence of risk in the dose range of 0 - 0.10 Sv. Doubling doses were calculated by the chromosome aberrations test for the somatic cells of bank vole and showed that the doubling dose estimates for acute irradiation of somatic cells of bank vole and human lymphocytes of peripheral blood as well as for germ cells in laboratory mice are close to each other. Therefore the choice of bank vole as a model species for assessing genetic risk of low-dose chronic irradiation in human is justified. Transgeneration accumulation of genome instability was found by chromosome aberration tests and embryonal lethality in bank vole populations exposed to low-dose chronic irradiation within 20-22 generations (1986-1996). This transgeneration long-term effect of chronic low-dose exposure is detrimental because the genomes of animals in distant generations are more sensitive to the impact of very low radiation doses, as compared to the genomes of animals in a few first generations. Evidently, non-targeted effects of ionizing radiation such as genomic instability, bystander effects and other new phenomena have to contribute to short-term and long-term overall outcome after low dose of radiation exposure. We believe that the increased thyroid cancer incidence of children from irradiated parents would be the first manifestation of the induced genomic instability. Reverse relationship between genetic effects induced by ionizing radiation in somatic cells of bank vole and whole-body absorbed dose rates was proved. The doubling dose under chronic irradiation with a very low dose rate of 2-40 μGy/day is 2.6 cGy while under acute irradiation with dose rate of 5 cGy/min the doubling dose is equal to 31.4 cGy. The estimated excess relative risk (ERR) per Sv for the selected dose ranges of Life Span Study Cohort was the highest for the lowest dose category, namely from 0 to 20 mSv in the comparison with dose range of 0-2 Sv

[en] According to data established in 1996, the frequencies of micronucleated erythrocytes in bone marrow and peripheral blood of bank vole (Clethrionomys glareolus, Schreber), whose populations have been lived in contaminated areas since 1986 depend on chronic low intensity irradiation (dose rates in the range from 2,4 to 41,3 mGy/day). The forms of these dose-effect relationships for the observed cytogenetic injuries are nonlinear and better described by the parabola equations. It is found that inducible repair system 'adaptive response' functions quite well within 21st-24th bank vole generations after the Chernobyl accident

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